Study On Radiation Transport And Related Radiation Fluid Dynamics

The interaction between high-temperature radiation field and matter is a fundamental problem in High-Energy-Density physics, astrophysics and Inertial Confinement Fusion (ICF). Due to the large difference in opacity and equation of state (EOS) between high-Z and low-Z materials, they show different radiation hydrodynamic behavior when they interact with high-temperature radiaton fields. In the system containing both high-Z and low-Z materials, two kinds of materials influence each other so that some particular radiation hydrodynamic phenomena are discussed such as mass-shell and confined ablation. Using one-dimension radiation hydrodynamic code RDMG, these radiation hydrodynamic processes are investigated, and several results are obtained as follows.1. Local thermal equilibrium (LTE) approximation is usually used in the simulation of radiation hydrodynamic processes. We have investigated the condition of LTE approximation under the influence of high-temperature radiation field. Also, we have analyzed the character of atomic processes which are dominated by collision and by radiation respectively. It is found out that when plasma is in low temperature and high density, the bound electrons would reach thermal equilibrium with free electrons quickly, and the plasma is in LTE state. On the contrary, when plasma is in high temperature and low density, the bound electrons would reach thermal equilibrium with radiation field, and the relaxation time with free electrons is much longer than that with radiation field. In this case the plasma is in quasi-LTE state.2. The emission behavior of high-Z wall is important to understand the radiation spectrum inside the tube. We have investigated the emission behavior of the surface of the high-Z materials. It is found that the gradient of temperature is the reason why the surface intensity emitted by high-Z plasma deviates from the equilibrium. Meanwhile, by solving the integral radiation transport equation, the formula to calculate the intensity emitted by high-Z plasma is obtained. Comparing the formula with simulation result, we find that the formula can characterize the emission of high-Z plasma with good precision. This formula can also be used in the calculation of the interface connection condition.3. In the research of confined ablation, the ablation process of gold wall and gold foil confined by CH foam is investigated. It is found that the influence of CH foam on gold wall (foil) is equivalent to a pressure boundary condition. Increasing the opacity factor of gold would slow down the gold wall expansion and increase the burn through time of gold foil. Meanwhile, increasing the EOS factor of gold would speed up the gold wall expansion and increase the burn through time of gold foil. On the basis of former research, a possible experimental method is proposed to determine the opacity factor and EOS factor of gold. 4. In the research of radiation cooling, we concentrate on the mass-shell phenomena. By studying several theoretical models, the physical reason of mass-shell is illustrated. The influence of initial parameters on the peak density, contrast and width of mass-shell is investigated. Also, how the mass-shell affects the flux of high-Z interface is studied. It is found that the work of the hydromotion is the major way to transfer energy between high-Z and low-Z matter in the radiation cooling process in the parameters region of ICF.